Display device and electronic apparatus

ABSTRACT

A display device is provided which offers double-sided display and achieves a thin structure and also which prevents deterioration in display quality of each of front and back display units when an illumination unit such as a backlight is shared by these display units. The display device includes a first display unit having a display surface on the front surface thereof; a second display unit having a display surface on the rear surface thereof; and a common illumination unit interposed between the first display unit and the second display unit, for illuminating both the first display unit and the second display unit with light. The illumination unit includes a light-guiding member having a first light-emitting surface opposed to the first display unit and a second light-emitting surface opposed to the second display unit, and a transflector is interposed between the second light-emitting surface of the light-guiding member and the second display unit.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a display device and anelectronic apparatus, and in particular, it relates to the structure ofa display device suitably mounted on a portable electronic apparatus.

[0003] 2. Related Art

[0004] In general, an electro-optical device such as a liquid crystaldisplay device or an electro-luminescent display device is used as adisplay device mounted on a portable electronic apparatus. Inparticular, a cellular phone has a compact liquid crystal display devicemounted in a small casing thereof. In recent years, a cellular phone ofa double-sided display type, having compact liquid crystal displaydevices mounted on the front and back of a thin displaying portionthereof, is commercially available on the market. Such a cellular phonehas a pair of liquid crystal display devices accommodated in thedisplaying portion of the casing thereof so as to lie back to back andplaced so as to be visible from both the front and back sides thereof.

[0005] Many liquid crystal display devices have a structure in which abacklight serving as an illuminator is disposed behind a liquid crystalpanel. Although a reflective liquid crystal display device having nosuch a backlight is available, its application is limited since itsdisplay is invisible in dark places and at night. Although the liquidcrystal display device equipped with a backlight has a drawback inthickness, with the recent advancements in higher definition and colordisplay of a compact liquid crystal display device, most portableelectronic apparatuses have them mounted thereon. In recent years, therehas emerged a transflective liquid crystal display device equipped witha backlight and able to perform both transmissive display and reflectivedisplay.

[0006] Since a portable electronic apparatus such as the above-mentionedcellular phone has become more compact and thinner year by year, a thinliquid crystal display device is strongly desired in accordance withthis trend. In order to meet this requirement, a thinner liquid crystalpanel and a thinner backlight are under development.

[0007] Unfortunately, the above-mentioned known cellular phone of adouble-sided display type has problems in that, since a pair of liquidcrystal display devices must be accommodated in its casing so as to lieback to back, it is hard to make the casing thinner, and, even when eachof the liquid crystal display devices is made thin, the casing isthicker and heavier than a normal portable phone of a single-sideddisplay type.

[0008] One method for solving the above problems lies in that a singlebacklight is shared by the front and back liquid crystal display devicesso as to illuminate a pair of front and back liquid crystal panels.Whereas, in a cellular phone of a double-sided display type, since thedisplay areas of the front and back liquid crystal display devices aregenerally different from each other, when a single backlight is sharedby them as mentioned above, the luminance distribution of a large mainpanel is affected by an illumination action of the backlight applied ona small sub-panel disposed behind the main panel, thereby causing a riskthat a shadow of the sub-panel is reflected in a display image of themain panel and thus its display quality deteriorates.

[0009] With this background, the present invention has been made inorder to solve the above problems. Accordingly, it is an object of thepresent invention to provide a display device which offers double-sideddisplay and achieves a thin structure and which prevents deteriorationin display quality of both front and back display units when anilluminator such as a backlight is shared by these display units.

SUMMARY OF THE INVENTION

[0010] In order to achieve the above-mentioned object, a display deviceaccording to the present invention includes a first display unit havinga display surface on the front surface thereof; a second display unithaving a display surface on the rear surface thereof; and a commonillumination unit interposed between the first display unit and thesecond display unit, for illuminating both the first display unit andthe second display unit with light. The illumination unit includes alight-guiding member including a first light-emitting surface oppositethe first display unit and a second light-emitting surface opposite thesecond display unit, and a transflector is interposed between the secondlight-emitting surface of the light-guiding member and the seconddisplay unit.

[0011] According to the present invention, with the common illuminationunit constructed so as to illuminate both the first display unit and thesecond display unit with light, one of two illumination units can beeliminated, thereby achieving a thinner and lighter device. Also, withthe transflector interposed between the second light-emitting surface ofthe light-guiding member of the illumination unit and the second displayunit, since part of light emitted from the second light-emitting surfaceof the light-guiding member is transmitted through the transflector andis then directed towards the second display unit, while the seconddisplay unit is constructed so as to be illuminated with light, theremaining light emitted from the second light-emitting surface of thelight-guiding member can be reflected at the transflector so as to bedirected towards the first display unit. Accordingly, it is possible toplace a priority on the illumination state of the first display unit,and hence the display quality of the first display unit can be improved.

[0012] Also, with the above structure, a transflector may also beinterposed between the first light-emitting surface and the firstdisplay unit. In this case, the second display unit also obtains anoptical effect equivalent to that of the first display unit.

[0013] In the display device according to the present invention, thedisplay area of the first display unit may extend so as totwo-dimensionally overlap the display area of the second display unitand an area lying outside the display area of the second display unit.With this structure, since the display area of the first display unitextends so as to two-dimensionally overlap not only the display area ofthe second display unit but also the area outside the display area ofthe second display unit, light emitted from the common illumination unittowards the second display unit causes the display feature of the firstdisplay unit to be optically affected due to the fact that the displayarea of the second display unit is present behind the first displayunit. Hence, a shadow of the display area of the second display unit issometimes reflected in the display surface of the first display unit.However, in the display device according to the present invention, sincethe transflector is interposed between the second light-emitting surfaceof the light-guiding member and the second display unit as describedabove, the optical affect caused by the second display unit can bereduced, and thus the display quality of the first display unit can beimproved.

[0014] In the display device according to the present invention, thetransflector may have a light-diffusing function. With this structure,the light-diffusing function improves the evenness of illumination lightfrom the illumination unit, thereby further preventing the unevenness ofdisplay of the first display unit and the second display unit. Inparticular, when the display device has a structure in which lightreflected at the transflector is diffused, the evenness of light in thelight-guiding member is improved, and the illuminance distribution onthe first display unit is made uniform, thereby further preventing theunevenness of display of the first display unit.

[0015] In the display device according to the present invention, thetransflector may have different optical characteristics between anoverlapping portion two-dimensionally overlapping the display area ofthe second display unit, of a region two-dimensionally overlappingbetween the transflector and the display area of the first display unit,and a portion of the region other than the overlapping portion. Withthis structure, the transflector has different optical characteristicsbetween the overlapping portion and the remaining portion of the region,thereby making the optical effects of the transflector applied on thedisplay area of the first display unit different between the overlappingportion and the remaining portion. Accordingly, an optical difference,for example, a difference in luminance levels, between the overlappingportion and the remaining portion in the display area of the firstdisplay unit can be reduced, or the display quality of the seconddisplay unit can be improved.

[0016] More particularly, in the case where the transflector is disposedacross the entire region, assuming that the second display unit isdisposed behind the overlapping portion of the region and another unitis disposed behind the portion other than the overlapping portion, whenthe transflector is formed so as to have uniform optical characteristicsacross the entire region, a difference in reflectances between thesecond display unit and the other unit causes a black shadow or a whiteshadow of the second display unit to be reflected in the display area ofthe first display unit. Accordingly, when the second display unit andthe other unit have a difference in reflectances therebetween like this,by making the optical characteristics of the transflector differentbetween the overlapping portion and the remaining portion as mentionedabove, the foregoing black or white shadow can be less noticeable.Meanwhile, the optical characteristics of the transflector meancharacteristics such as a light reflectance, a light transmittance, alight absorptance, and a light-diffusing rate, possibly affecting thedisplay features of the first display unit and the second display unit.

[0017] In the display device according to the present invention, thetransflector is preferably a thin film composed of a reflective materialand having a thickness allowing light to be substantially transmittedtherethrough. With this structure, since the transflector is providedwith a light transmittivity by adjusting the thickness of a thin filmcomposed of a reflective material, a step such as patterning can beeliminated, thereby easily making the transflector. A thin metal film ispreferred as the reflective material. In particular, aluminum, analuminum alloy, silver, a silver alloy, and the like are preferable asthe reflective material.

[0018] In the display device according to the present invention, thetransflector is preferably a thin film composed of a reflective materialand having a plurality of fine apertures dispersed therein such thatlight is substantially transmitted therethrough. With this structure,since the transflector is provided with a light transmittivity by havingthe fine apertures dispersed in a thin film composed of a reflectivematerial, the light transmittance is accurately controlled by changingthe aperture area ratio of the apertures, for example, by changing thesize and the density of the apertures.

[0019] In the display device according to the present invention, thetransflector may be formed by a base member composed of a lighttransmissive material and a light-diffusing layer having fine particlesdispersed in the base member and composed of a light transmissivematerial having a different refractive index from that of the basemember. With this structure, the transmittivity and the reflectivity ofthe transflector can be adjusted by changing a difference in refractiveindexes between the base material and the fine particles and also bychanging the size and the density of the fine particles, and also, theunevenness of display can be prevented by the light-diffusing effects ofthe transflector. In particular, with this structure, the transmittanceof the transflector can be easily made higher.

[0020] In the display device according to the present invention, thetransflector may be formed by a base member composed of a lighttransmissive material and a light-diffusing layer having fine particlesdispersed in the base member and composed of a reflective material. Withthis structure, since light is diffused by the fine particles dispersedin the base member and composed of a reflective material, thetransmittivity and the reflectivity of the transflector can be adjustedby changing the size and the density of the fine particles, and also,the unevenness of display can be prevented by the light-diffusingeffects of the transflector. In particular, with this structure, thereflectance of the transflector can be easily made higher.

[0021] In the display device according to the present invention, a lightdiffuser may be interposed between the first light-emitting surface ofthe light-guiding member and the first display unit. With thisstructure, since the light diffuser is interposed between the firstlight-emitting surface and the first display unit, the evenness of theilluminance distribution of the illumination unit can be improved,thereby further preventing the unevenness of display of the firstdisplay unit.

[0022] Meanwhile, the light diffuser may be formed so as to havedifferent optical characteristics between the overlapping portiontwo-dimensionally overlapping the display area of the second displayunit, of the region two-dimensionally overlapping the display area ofthe first display unit, and the portion of the region other than theoverlapping portion. With this structure, the unevenness of display ofthe first display unit can be further prevented.

[0023] The light diffuser may be formed by a base member composed of alight transmissive material and a light-diffusing layer having fineparticles dispersed in the base member and composed of a lighttransmissive material having a different refractive index from that ofthe base member. Alternatively, the light diffuser may be formed by abase member composed of a light transmissive material and alight-diffusing layer having fine particles dispersed in the base memberand composed of a reflective material. Further alternatively, the lightdiffuser may be formed by a light diffusing layer composed of a lighttransmissive material and having a structure in which fine undulationsare formed on the surface thereof.

[0024] Next, an electronic apparatus according to the present inventionpreferably includes any one of the above-mentioned display devices andcontrollers for controlling the display device. Especially, as the aboveelectronic apparatus, a portable electronic apparatus is effective fromthe viewpoint of easily achieving a thin casing thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a sectional view schematically illustrating thestructure of a display device according to a first embodiment of thepresent invention.

[0026] FIGS. 2(a) to 2(e) are sectional views schematically illustratingthe structures of a transflector according to the first embodiment.

[0027] FIGS. 3(a) and 3(b) are plan views schematically illustrating thestructures of a transflector according to a second embodiment of thepresent invention.

[0028] FIGS. 4(a) and 4(b) are plan views schematically illustrating thestructures of a transflector according to a third embodiment of to thepresent invention.

[0029] FIGS. 5(a) and 5(b) are sectional views schematicallyillustrating the structures of display devices according to a fourthembodiment of to the present invention.

[0030]FIG. 6 is a structural block diagram illustrating the structure ofan example electronic apparatus.

[0031] FIGS. 7(a) and 7(b) are perspective views schematicallyillustrating the structure of a cellular phone serving as the exampleelectronic apparatus.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] Referring now to the accompanying drawings, preferred embodimentsof display devices and an electronic apparatus according to the presentinvention will be described in detail.

[0033] First Embodiment

[0034] Referring first to FIG. 1, a liquid crystal display device 100according to a first embodiment of the present invention will bedescribed. The liquid crystal display device 100 includes a firstdisplay unit 110, a second display unit 120, and an illumination unit130.

[0035] The first display unit 110 is a liquid crystal panel and isformed such that substrates 111 and 112 composed of glass or plastic arebonded to each other via a sealant 113 and have liquid crystal 114interposed therebetween. The liquid crystal 114 is formed so as toreceive predetermined electrical fields with electrodes formed on theinner surfaces of the substrates 111 and 112. The substrate 112 has apolarizer 115 disposed on the outer surface thereof, that is, on thefront surface side or on the observing side of the first display unit,and the substrate 111 also has the polarizer 116 disposed on the outersurface thereof, that is, on the back surface side.

[0036] The second display unit 120 is also a liquid crystal panel and isformed such that substrates 121 and 122 composed of glass or plastic arebonded to each other via a sealant 123 and have liquid crystal 124interposed therebetween. The liquid crystal 124 is formed so as toreceive predetermined electrical fields with electrodes formed on theinner surfaces of the substrates 121 and 122. The substrate 122 has apolarizer 125 disposed on the outer surface thereof, that is, on theback surface side or the observing side of the second display unit, andthe substrate 121 has a polarizer 126 on the outer surface thereof, thatis, on the front surface side.

[0037] The first display unit 110 and the second display unit 120 havethe illumination unit 130 interposed therebetween. The illumination unit130 serves as a backlight. The illumination unit 130 includes a lightsource 131 formed by, for example, a cold cathode fluorescent tube or alight emitting diode (LED), and a light guiding plate 132 receivinglight emitted from the light source 131. The light guiding plate 132 iscomposed of a transparent material such as an acrylic resin. In theillumination unit 130, the light guiding plate 132 is a plate disposedso as to be orthogonal to an optical-axis direction of the displaydevice, and the light source 131 is disposed along a side surface of thelight guiding plate 132. The light guiding plate 132 is disposed suchthat a light incident surface 132 a serving as a side surface thereof isopposed to the light source 131, a first light-emitting surface 132 bserving as a front surface thereof, that is, an upper surface thereof inthe figure, faces the first display unit 110, and a secondlight-emitting surface 132 c serving as a back surface thereof in thefigure, faces the second display unit 120.

[0038] The light guiding plate 132 is formed so as to outputillumination light from the first light-emitting surface 132 b towardthe first display unit 110 and also to output illumination light fromthe second light-emitting surface 132 c toward the second display unit120 while allowing light received from the light source 131 to propagatetherein. In the light guiding plate 132, light incident on the firstlight-emitting surface 132 b and the second light-emitting surface 132 cat an angle smaller than a critical angle is subjected to totalreflection, and light incident on the same at the critical angle orgreater is outputted outside from the first light-emitting surface 132 band the second light-emitting surface 132 c. Especially, although notshown in the figure, either or both the first light-emitting surface 132b and the second light-emitting surface 132 c may have undulatedsurfaces or scattering layers formed thereon serving as opticaldeflectors for outputting the light introduced from the light source 131along or close to the optical axis directions of the first display unit110 and the second display unit 120.

[0039] The second light-emitting surface 132 c of the light guidingplate 132 and the second display unit 120 have a transflector 141interposed therebetween. The transflector 141 suffices to have astructure in which part of illumination light from the illumination unitis reflected towards the front surface side and at least part of theremaining illumination light is transmitted therethrough towards theback surface side. Also, the transflector is made from, for example, athin metal film or a metal film having a large number of fine aperturesdispersed therein. In addition, the transflector 141 may be disposedwhile being bonded to the rear surface of the light guiding plate 132 ormay be formed from a sheet or a plate independent of the light guidingplate 132. Meanwhile, although the transflector according to the presentinvention suffices to be interposed between the second light-emittingsurface 132 c of the illumination unit 130 and the second display unit120 and has no limitations other than this, the following description isbased on the assumption that the transflector 141 according to thepresent embodiment is basically formed so as to entirely cover thesecond light-emitting surface 132 c of the light guiding plate 132 andto have two-dimensionally-uniform optical characteristics.

[0040]FIG. 2 illustrates example structures of the foregoingtransflector 141. In the transflector having the example structure shownin FIG. 2(a), a reflective thin film 141B composed of a reflectivematerial, for example, metal such as aluminum is formed on the frontsurface of a transparent substrate 141A composed of glass, a plasticfilm, or the like. White pigment such as white resin and titanium oxide,metals such as aluminum and silver, and so forth are preferred as thereflective material. The transflector having this example structure maybe formed such that the light guiding plate 132 is used instead of theforegoing transparent substrate 141A and that the reflective thin film141B is formed on the second light-emitting surface 132 c. This applieslikewise to the transflector having the other structures shown in FIGS.2(b) to 2(e).

[0041] By making a thin film from metal such as aluminum or silver so asto have a thickness of about 10 nm to 50 nm, the reflective thin film141B has an average transmittance of about 30% to 70% in a visible lightrange as its optical characteristic. The above thin film is formed bydeposition, sputtering, laser ablation, or the like. The reflectance andthe transmittance of the transflector having this example structure canbe adjusted by changing the film thickness.

[0042] Also, the transflector may be made from a known dielectricmultilayer film instead of the reflective material as mentioned above.

[0043] In the transflector having the example structure shown in FIG.2(b), a reflective thin film 141C composed of a reflective material, forexample, metal such as aluminum is formed on the front surface of thetransparent substrate 141A. White pigment such as white resin andtitanium oxide, metal such as aluminum and silver, and so forth arenamed as the reflective material. The reflective thin film 141C isformed so as to have an average reflectance of about 90% or more as awhole in the visible light range and also to have a large number of fineapertures 141Ca formed therein. The fine apertures 141Ca are dispersedover the entire surface of the reflective thin film 141C. An equivalentaperture diameter of each fine aperture 141Ca, that is, an aperturediameter of a round aperture having the same area as that of the fineaperture, is preferably about 1 μm to 100 μm, and is more preferablyabout 5 μm to 30 μm. Especially, the fine apertures are preferablyformed so as to be smaller than the sizes of pixels of the first andsecond display units and also to be spaced at intervals smaller than thepitches of the pixels. The reflectance and the transmittance of thetransflector having this example structure can be adjusted by changingthe aperture area ratio of the fine apertures 141Ca. The aperture arearatio is determined by the equivalent aperture diameter and the formeddensity of the fine apertures 141Ca.

[0044] In the transflector having the example structure shown in FIG.2(c), a light-diffusing layer 141D basically composed of a lighttransmissive material is formed on the front surface of the transparentsubstrate 141A. The light-diffusing layer 141D includes a transparentsubstrate 141 d 1 composed of acrylic resin or the like and fineparticles 141 d 2 dispersed in the substrate 141 d 1. The substrate 141d 1 and the fine particles 141 d 2 are composed of materials havingdifferent refractive indexes from each other. Particles composed ofsilica, acrylic resin, and the like are named as the fine particles. Thediameters of the particles are preferably about 1 μm to 10 μm, and morepreferably about 4 μm to 5 μm.

[0045] In the transflector having this example structure, since theparticles having different refractive indexes from each other aredispersed in the substrate, light is scattered or dispersed in amacroscopic view, whereby the transflector having this example structureexhibits optical characteristics reflecting part of the light andtransmitting the remaining light therethrough. The reflectance and thetransmittance of the transflector having this example structure can beadjusted by changing a difference in refractive indexes between thesubstrate and the particles, the size and the distribution density ofthe particles, and the like.

[0046] In the transflector having the example structure shown in FIG.2(d), a light-diffusing layer 141E basically composed of a lighttransmissive material is formed on the front surface of the transparentsubstrate 141A. The light-diffusing layer 141E includes a transparentsubstrate 141 e 1 composed of acrylic resin or the like and lightreflective fine particles 141 e 2 dispersed in the substrate 141 e 1.The fine particles 141 e 2 are composed of a reflective material. Whitepigment such as white resin and titanium oxide, metal such as aluminumand silver, and so forth are preferred as the reflective material. Thediameters of the particles 141 e 2 are preferably about 1 μm to 10 μm,and more preferably about 2 μm to 3 μm.

[0047] In the transflector having this example structure, since theparticles composed of a reflective material are dispersed in thesubstrate, light is scattered or dispersed in a macroscopic view,whereby the transflector having this example structure exhibits opticalcharacteristics reflecting part of the light and transmitting theremaining light therethrough. The reflectance and the transmittance ofthe transflector having this example structure can be adjusted bychanging the reflectance, the size, and the density of the particles,and the like.

[0048] In the transflector having the example structure shown in FIG.2(e), the reflective thin film 141B, the same as that shown in FIG. 2(a)composed of a reflective material, is formed on the front surface of thetransparent substrate 141A, and a diffusing layer 141F composed of alight transmissive material, preferably of a transparent material, andhaving fine undulations on the surface thereof is additionally formed onthe thin film 141B. The surface undulation of the diffusing layer 141Fhas a depth of about 2 μm to 3 μm formed at an interval of, for example,about 1 μm to 10 μm, preferably about 3 μm to 4 μm. This surfaceundulation is formed by patterning such as photolithography. Forexample, the above-mentioned surface undulation is formed such thatafter application on the reflective thin film 141B, a transparentphotosensitive resin is exposed with a mask pattern having openingsformed with an interval corresponding to the above-mentioned surfaceundulation and is then developed. Meanwhile, a step of additionallyapplying an additional transparent resin on the foregoing developedtransparent resin or heating the developed transparent resin so as to besoftened may be added so as to provide a smooth surface undulation.

[0049] According to this example structure, the transflector obtainsreflection and transmission characteristics in accordance with thethickness of the reflective thin film 141B in the same fashion asmentioned above, and also is provided with a light-diffusing functionsince light incident on and reflected at the reflective thin film 141Bis scattered by the diffusing layer 141F, thereby improving the evennessof the luminance distributions of the first display unit 110 and thesecond display unit 120.

[0050] Also, the light guiding plate 132 and the first display unit 110have a light diffuser 142 interposed therebetween. The light diffuser142 is intended to prevent the unevenness of display, that is, theuneven brightness across the display surface of the fist display unit,caused by the structures of the light guiding plate 132 and the othercomponents lying on the back surface side thereof, that is, lying on thelower side in the figure, by appropriately diffusing light emitted fromthe light guiding plate 132. The light diffuser 142 may have an examplestructure in which fine particles composed of an acrylic resin or thelike and having an example diameter of about 2 μm to 3 μm are dispersedin a base material composed of an acrylic resin or the like having adifferent refractive index from that of the fine particles, or in whichfine undulations are provided on the surface thereof. More particularly,the light diffuser 142 may have the same structure as those shown inFIG. 2(c) or 2(d), or a structure formed by removing the reflective thinfilm 141B from the structure shown in FIG. 2(e). The light diffuser 142may be disposed while being bonded to the front surface of the lightguiding plate 132 or may be formed from a sheet or a plate independentof the light guiding plate 132.

[0051] Also, a light diffuser 145 is interposed between the lightguiding plate 132 and the second display unit 120, and is interposedbetween the transflector 141 and the second display unit 120 accordingto the present embodiment. The light diffuser 145 has the same structureas that of the light diffuser 142.

[0052] Meanwhile, in the present embodiment, since an overlappingportion, lying in a region two-dimensionally overlapping the displayarea of the first display unit 110 and two-dimensionally overlapping thedisplay area of the second display unit 120, and the remaining portionlying in the region have different optical structures from each other,in order to improve the evenness of the display surface of the firstdisplay unit, the foregoing light diffuser may be formed such that theoverlapping portion and the remaining portion have different diffusionrates, for example, haze values, from each other.

[0053] In the present embodiment, in order to increase the percentage oflight substantially contributing to display in each of the first displayunit 110 and the second display unit 120, light collectors 143 and 144,that is, prism sheets 143 and 144 are interposed between theillumination unit 130 and the first display unit 110, and lightcollectors 146 and 147, that is, prism sheets 146 and 147 are interposedbetween the illumination unit 130 and the second display unit 120. Eachlight collector has a prism surface for refracting light so as to directthe light along or close to an optical-axis direction of the displaydevice, that is, the vertical direction in the figure. Moreparticularly, the prism surface is formed by a plurality of ribs/convexportions, each having a triangular cross section, juxtaposed with eachother in a stripe pattern on the surface of the corresponding collector.The light collectors 143 and 144 as well as the light collectors 146 and147 are disposed such that the foregoing corresponding ribs extend alongdirections substantially perpendicular to each other.

[0054] Next, an operation of the display device according to the presentembodiment and having the above-described structure will be described.In the following description, for simplicity of description, it isassumed that both the first display unit 110 and the second display unit120 serving as liquid crystal panels are formed so as to perform displayin a TN-type liquid crystal mode, that the polarizer 115 transmitslinearly polarized light A having a plane of vibration parallel to theplane of the figure, that is, first polarized light, and reflectslinearly polarized light B having a plane of vibration orthogonal to theplane of the figure, that is, second polarized light, and that thepolarizer 116 transmits the linearly polarized light B, that is, thirdpolarized light, and absorbs the linearly polarized light A, that is, afourth polarized light. In addition, it is assumed that the polarizer125 transmits the linearly polarized light A and absorbs the linearlypolarized light B, and that the polarizer 126 transmits the linearlypolarized light B and absorbs the linearly polarized light A. That is,although directional relationships among the planes of vibration of thefirst polarized light to the fourth polarized light are generallyarbitrary, in the following description, the first polarized light andthe fourth polarized light exhibit the same polarized state as eachother, and the second polarized light and the third polarized lightexhibit the same polarized state as each other.

[0055] Light emitted from the light source 131 is introduced in thelight guiding plate 132 and is emitted little by little therefromtowards the front and back surface sides while propagating in the lightguiding plate 132. First, illumination light emitted towards the firstdisplay unit 110 passes through the light diffuser 142, becomes thelinearly polarized light B upon passing through the polarizer 116,passes through the light collectors 143 and 144, and is then incident onthe liquid crystal 114. When the liquid crystal 114 is in an OFF-state,upon passing through the liquid crystal 114, the illumination lightbecomes the linearly polarized light A due to the optical rotary powerof the liquid crystal, passes through the polarizer 115, and is emittedtowards the front surface side as transmissive light T1. When the liquidcrystal 114 is in an ON-state, since the illumination light remains asthe linearly polarized light B even when passing through the liquidcrystal 114, it is absorbed by the polarizer 115.

[0056] In the meantime, external light incident on the first displayunit 110 becomes the linearly polarized light A upon passing through thepolarizer 115 and is incident on the liquid crystal 114. When the liquidcrystal 114 is in an OFF-state, the external light becomes the linearlypolarized light B, is transmitted through the polarizer 116, and entersthe light guiding plate 132, and then, part of this light is reflectedat the transflector 141, becomes the linearly polarized light A uponpassing again through the polarizer 116 and the liquid crystal 114, istransmitted through the polarizer 115, and is emitted as reflectivelight RD1. Also, when the liquid crystal 114 is in an ON-state, sincethe linearly polarized light A of the external light passing through thepolarizer 115 remains as the linearly polarized light A even whenpassing through the liquid crystal 114, it is absorbed by the polarizer116.

[0057] Meanwhile, when the foregoing light collectors 143 and 144 aredisposed, since external light is scattered upon being incident on theselight collectors, the reflective light RD1 is not substantiallyobtained. Accordingly, when it is expected to effectively use theforegoing reflective light RD1, it is preferable that none of theselight collectors be disposed.

[0058] Next, part of illumination light emitted from the illuminationunit 130 towards the second display unit 120 is transmitted through thetransflector 141, passes through the light diffuser 145, becomes thelinearly polarized light B upon passing through the polarizer 126, andpasses through the liquid crystal 124. When the liquid crystal 124 is inan OFF-state, upon passing through the liquid crystal 124, the linearlypolarized light B becomes the linearly polarized light A, is transmittedthrough the polarizer 125, and is emitted as transmissive light T2towards the back surface side. When the liquid crystal 124 is in anON-state, since the linearly polarized light B remains as it is evenwhen passing through the liquid crystal 124, it is absorbed thepolarizer 125.

[0059] In the meantime, of external light incident on the second displayunit 120, the linearly polarized light A is transmitted through thepolarizer 125 and is incident on the liquid crystal 124. When the liquidcrystal 124 is in an OFF-state, the linearly polarized light A becomesthe linearly polarized light B and passes through the polarizer 126 andthe light diffuser 143, and then, part of this light is reflected at thetransflector 141 while other part of the light is introduced in thelight guiding plate 132. The linearly polarized light B reflected at thetransflector 141 passes through the light diffuser 145 and the polarizer126 as it is, becomes the linearly polarized light A upon passing againthrough the liquid crystal 124, is transmitted through the polarizer125, and is emitted as reflective light RD2. When the liquid crystal 124is in an ON-state, since the above-mentioned linearly polarized light Aremains as it is even when passing through the liquid crystal 124, it isabsorbed by the polarizer 126.

[0060] Meanwhile, when the foregoing light collectors 146 and 147 aredisposed, since external light is scattered upon being incident on theselight collectors, the reflective light RD2 is not substantiallyobtained. Accordingly, when it is expected to effectively use theforegoing reflective light RD2, it is preferable that none of theselight collectors be disposed.

[0061] As described above, in the present embodiment, the first displayunit 110 performs display with the transmissive light T1 and thereflective light RD1. Also, the second display unit 120 performs displaywith the transmissive light T2 and the reflective light RD2. Thepresence of the reflective light RD1 and the reflective light RD2prevents deterioration in visibility of display in the case of observingan object at a bright place like outdoors or in the case of cutting anamount of illumination light of the illumination unit 130.

[0062] In the present embodiment, the illumination unit 130 is formed soas to emit light towards both the first display unit 110 and the seconddisplay unit 120, and in particular, the light guiding plate 132interposed between the first display unit 110 and the second displayunit 120 is shared by them, thereby making the overall structure of thedisplay device 100 thin and light. Also, with the transflector 141disposed as mentioned above, light in the light guiding plate 132 can bedivided towards both the first display unit 110 and the second displayunit 120 respectively disposed on the front and back sides, the evennessof illumination light emitted from the light guiding plate 132 towardseach of the front and back sides can be improved, and also, externallight incident on the first display unit 110 and the second display unit120 can be reflected at the transflector so as to serve as part ofdisplay light.

[0063] In particular, with the presence of the transflector 141, theilluminance distribution of the illumination unit 130 on the firstdisplay unit 110 is unlikely to be optically affected by the presence ofthe second display unit 120. With this structure, even when the displayarea of the first display unit 110 is set greater than that of thesecond display unit 120 as shown in the figure, a shadow of the displayarea of the second display unit 120 is unlikely to be reflected in thedisplay surface of the first display unit 110, thereby improving thedisplay quality of the first display unit 110.

[0064] Meanwhile, as mentioned above, although the display areas of thefirst and second display units 110 and 120 overlap with each other, inthe case where the one includes the other or in the case where the twodisplay areas do not partially overlap with each other, the unevennessof display becomes generally noticeable. Hence, the above-describedstructure is especially effective in these cases. However, regardless ofthe above-mentioned cases, when a common illuminator is used toilluminate the display units lying on both the front and back sides, theunevenness of the illuminance distribution of the illumination unit isin general likely to occur. Hence, different from the above cases, evenwhen both the display areas have almost the same size as each other andoverlap so as to align two-dimensionally with each other, the structureof the display device according to the present invention is technicallyeffective in order to achieve the evenness of the luminance of each ofthe display units.

[0065] Second Embodiment

[0066] Referring next to FIG. 3, a display device according to a secondembodiment of the present invention will be described. Since the displaydevice according to the second embodiment basically has the samestructure as that of the display device according to the firstembodiment shown in FIG. 1 except for its transflector, illustrationsand descriptions of the same parts in the second embodiment will beomitted.

[0067] As shown in FIG. 3(a), a transflector 241 according to thepresent embodiment is interposed between the second light-emittingsurface 132 c of the light guiding plate 132 and the second display unit120 so as to entirely cover a region AR1 two-dimensionally overlappingthe display area of the first display unit 110. The transflector 241 hasan overlapping portion AR2 which two-dimensionally overlaps the displayarea of the second display unit 120 and which serves as an aperture241A, and in the region AR1, a portion AR3 other than the overlappingportion AR2 serves as a reflector 241R reflecting visible light.

[0068] With this structure, the second display unit 120 is illuminatedwith light emitted from the light guiding plate 132 and passing throughthe aperture 241A, thereby easily achieving bright display of the seconddisplay unit 120. Also, with respect to the first display unit 110,since substantially all light is reflected at the portion AR3, an amountof light contributing to display as a whole can be increased. However,in this case, since the intensity of the illumination light illuminatingthe first display unit 110 decreases in the overlapping portion AR2, itis preferable that the display device preferably have a structure inwhich the intensity distribution of the illumination light can bemodified by adjusting a light-diffusing effect of the light diffuser142, a light-emitting distribution of the light guiding plate 132, andthe like.

[0069]FIG. 3(b) illustrates a modification of the present embodiment. Atransflector 241′ according to the modification is formed such that alarge number of fine apertures 241A′ are dispersed in the reflectivesurface of the overlapping portion AR2 and that a portion other than theoverlapping portion AR2 has no apertures and serves as the reflector241R′ reflecting light. In this modification, the second display unit120 is illuminated with light passing through the fine apertures 241A′formed in the overlapping portion AR2. However, in the overlappingportion AR2, since light is reflected at the reflective surface otherthan the fine apertures 241A′ towards the first display unit 110, adifference in brightness of display between two parts of the displaysurface of the first display unit 110 respectively corresponding to theoverlapping portion AR2 and the remaining portion AR3 can be reduced.Meanwhile, also in this case, in order to further prevent the unevennessof display of the first display unit 110, it is preferable that thedisplay device have a structure in which the intensity distribution ofthe illumination light can be modified by adjusting a light-diffusingeffect of the light diffuser 142, a light-emitting distribution of thelight guiding plate 132, and the like.

[0070] Third Embodiment

[0071] Referring next to FIG. 4, a display device according to a thirdembodiment of the present invention will be described. Since the displaydevice according to the present embodiment basically has the samestructure as that of the display device according to the firstembodiment shown in FIG. 1 except for its transflector, illustrationsand descriptions of the same parts in the third embodiment will beomitted.

[0072] As shown in FIG. 4(a), in the region AR1, a transflector 341 isformed such that the overlapping portion AR2 is composed of atransflective material 341A having a predetermined reflectance andtransmittance, for example, both in the range from 30 to 70%, and theportion AR3 other than the overlapping portion AR2 is composed of areflective material 341B having a lower transmittance than that of theoverlapping portion AR2 while having substantially the same reflectanceas that of the overlapping portion AR2, for example, in the range from30 to 70%. It is preferable that the transmittance of the reflectivematerial 341B of the portion AR3 be nearly 0%. Such a material is easilyobtained, especially from a dielectric multilayer film.

[0073] With this structure, the overlapping portion AR2 in the regionAR1 allows illumination light emitted from the illumination unit 130 tobe reflected towards the first display unit 110 and to be transmittedtherethrough towards the second display unit 120 at the same time,whereby both display units can be illuminated at the same time. Inaddition, the portion AR3 other than the overlapping portion AR2 doesnot allow unnecessary light to be transmitted therethrough towards theback thereof because of its low transmittance, and also, since thereflectance of the portion AR3 is substantially the same as that of theoverlapping portion AR2, the unevenness of display of the first displayunit 110 can be prevented.

[0074] According to this example structure, when it is intended toremove the unevenness of display of the first display unit 110, a lightloss of illumination light due to absorption by the portion AR3 isgenerated, whereby a light utilization efficiency of the display deviceas a whole decreases. In order to improve the light utilizationefficiency, it is necessary to reduce the light loss in the portion AR3by making the reflectance of the portion AR3 higher relative to that ofthe overlapping portion AR2, and it is preferable that the unevenness ofdisplay of the first display unit 110 possibly caused by thisarrangement be modified by changing the structures of the light-guidingplate 132, the light diffuser 142, and so forth.

[0075]FIG. 4(b) illustrates a modification of the present embodiment. Anentire transflector 341′ is composed of a reflective material. Thetransflector 341′ has a large number of fine apertures 341A′ dispersedin the overlapping portion AR2, and, in place of the fine apertures341A′, also has fine absorbers 341B′ composed of a black resin or thelike and dispersed in the portion AR3 other than the overlapping portionAR2.

[0076] The transflector 341′ has a structure in which the fine apertures341A′ in the overlapping portion AR2 allow the second display unit 120lying at the back thereof to be illuminated with light, and also thefine absorbers 341B′ formed in the remaining portion AR3 reduce adifference in reflectances between the overlapping portion AR2 and theportion AR3. With this structure, the unevenness of display of the firstdisplay unit 110 can be prevented.

[0077] Fourth Embodiment

[0078] Referring next to FIG. 5, a display device according to a fourthembodiment of the present invention will be described. The displaydevice according to the present embodiment has a structure in which anyone of the display devices according to the foregoing embodiments isaccommodated in a casing composed of a synthetic resin, or the like.Accordingly, since the display device of the present embodimentbasically has the same structure as that of the display device accordingto the first embodiment shown in FIG. 1 except for its structuralfeature of accommodation with the casing, illustrations of the sameparts in the present embodiment will be simplified and descriptions ofthe same parts will be omitted.

[0079] As shown in FIG. 5(a), a display device 100′ includes the firstdisplay unit 110, the second display unit 120, the illumination unit130, and the other foregoing components (not shown), which are the sameas those of each of the display devices according to the foregoingembodiments, and these components are accommodated in a casing 150. Thecasing 150 is composed of, for example, a white synthetic resin. Makingthe casing 150 from a white material is preferable from the viewpoint ofimproving a utilization efficiency of illumination light of theillumination unit 130 since this casing reflects light leaked from thelight guiding plate 132 and returns again to the light guiding plate132.

[0080] In the present embodiment, an area not having the second displayunit 120 disposed therein, on the front surface of the secondlight-emitting surface of the light guiding plate 132 of theillumination unit 130, that is, the foregoing portion AR3, has anoptical sheet 151 having predetermined optical characteristics anddisposed therein. When viewed from the first display unit 110, theoptical sheet 151 is composed of a material having substantially thesame reflectance as that of the second display unit 120. With thisstructure, even when the transflector 141 has entirely uniform opticalcharacteristics, the unevenness of display of the display surface of thefirst display unit can be decreased.

[0081]FIG. 5(b) illustrates a modification of the present embodiment. Ina display device 100″ according to this modification, the first displayunit 110, the second display unit 120, the illumination unit 130, andthe other components (not shown), which are the same as those of each ofthe display devices according to the foregoing embodiments, areaccommodated in a casing 160. When viewed from the first display unit110, the casing 160 is composed of a material exhibiting substantiallythe same reflectance as that of the second display unit 120. With thisstructure, even when the foregoing transflector 141 has entirely uniformoptical characteristics, the unevenness of display of the displaysurface of the first display unit can be decreased.

[0082] Meanwhile, the optical sheet 151 and the casing 160 suffice to beformed such that, when observed from the first display unit 110 via theillumination unit 130, the illuminance distributions of a portion wherethe display area of the second display unit 120 presents and anotherportion where the optical sheet 151 and the casing 160 are disposed aremutually made uniform regardless of the structures of the transflector141 and the light guiding plate 132.

[0083] Fifth Embodiment

[0084] Referring next to FIGS. 6 and 7, an electronic apparatus,including the display device 100 according to the first embodiment, willbe described. As shown in FIG. 6, the electronic apparatus according tothe present embodiment includes a controller 1100 for controlling thefirst display unit 110, that is, the liquid crystal display panel 110,and a controller 1200 for controlling the second display unit 120, thatis, the liquid crystal display panel 120. The controllers 1100 and 1200are controlled by a central controller 1000 disposed in the electronicapparatus and formed by a microcomputer and so forth.

[0085] The first and second display units 110 and 120 are respectivelyconnected to drive circuits 110D and 120D including semiconductor ICsand the like, which are mounted on the corresponding panels or connectedto the corresponding panels via respective wiring members, and thesedrive circuits 110D and 120D are respectively connected to thecontrollers 1100 and 1200. The controllers 1100 and 1200 respectivelyinclude display-information output sources 1110 and 1210,display-information process circuits 1120 and 1220, power supplycircuits 1130 and 1230, and timing generators 1140 and 1240.

[0086] Each of the display-information output sources 1110 and 1210includes a memory such as a read only memory (ROM) and/or a randomaccess memory (RAM), a storage unit such as a magnetic storage diskand/or an optical storage disk, and a tuning circuit for outputting atuned digital image signal. Also, in response to a variety of clocksignals generated by the timing generators 1140 and 1240, thedisplay-information output sources 1110 and 1210 supply displayinformation, in the form of an image signal according to a predeterminedformat or the like, to the display-information process circuits 1120 and1220, respectively.

[0087] Each of the display-information process circuits 1120 and 1220includes a variety of known circuits such as a serial-parallelconversion circuit, an amplification and reversion circuit, a rotationcircuit, a gamma correction circuit, and a clamp circuit, processes theinput display information, and supplies the processed image informationtogether with a clock signal CLK to the corresponding drive circuit.Each of the drive circuits 110D and 120D includes a scan-line drivecircuit, a data-line drive circuit, and a testing circuit. Also, each ofthe power supply circuits 1130 and 1230 supplies a predetermined voltageto each of the above described corresponding components.

[0088] The central controller 1000 sends original data for illuminationlights-on and -off commands and display information, and the like, ifneeded, to the display-information output sources 1110 and 1210 of thecorresponding controllers 1100 and 1200, controls thedisplay-information output sources 1110 and 1210 so as to output displayinformation in response to the original data and the like, and alsocontrols the first display unit 110 and the second display unit 120 soas to display required display images via the controllers 1100 and 1200and the drive circuits 110D and 120D, respectively. Also, the centralcontroller 1000 is formed so as to control the illumination lights-onand -off, and the like of the light source 131.

[0089]FIG. 7 illustrates a cellular phone 2000 serving as an example ofthe electronic apparatus according to the present invention. Thecellular phone 2000 includes a main body 2001 having a variety ofbuttons disposed thereon and a microphone housed therein, and a displayunit 2002 having a display screen and an antenna mounted thereon and aspeaker housed therein, and the main body 2001 and the display unit 2002are constructed so as to be mutually foldable. The display unit 2002 hasthe display device 100 housed therein, while having the display screenof the first display unit 110 disposed on the inner surface thereof soas to be visible and also the display screen of the second display unit120 disposed on the outer surface thereof so as to be visible.

[0090] In the present embodiment, as shown in FIG. 7(a), when thedisplay unit 2002 is opened by separating from the main body 2001, inresponse to a command from the central controller 1000, the firstdisplay unit 110 is illuminated, and a predetermined image is displayed.Also, as shown in FIG. 7(b), when the display unit 2002 is folded ontothe main body 2001, the first display unit 110 is illuminationlights-off, the second display unit 120 is illuminated instead of theabove illumination lights-off, and a predetermined image is displayed.

[0091] In the present embodiment, the display device 100 having a thinstructure as mentioned above allows the display unit 2002 to have a thinstructure, to have a simple internal structure, and to be easilyassembled. Meanwhile, the electronic apparatus according to the presentembodiment may also have any one of the display devices in the second tofourth embodiments mounted thereon.

[0092] Meanwhile, the electro-optical device and the electronicapparatus according to the present invention are not limited to theforegoing example illustrations, and those skilled in the art willappreciate that a variety of modifications can be possible withoutdeparting from the spirit of the present invention. For example,although a liquid crystal display panel is used as an electro-opticalpanel in each of the foregoing embodiments, any one of a variety ofelectro-optical panels such as an organic electro-luminescence panel, aplasma display panel, and a field-emission display panel may also beused as the electro-optical panel according to the present invention.Also, although the liquid crystal display panel of a passive matrix typeis basically illustrated in the foregoing embodiments, the presentinvention is likewise applicable to that of an active matrix type.

[0093] The entire disclosure of Japanese Patent Application No.2002-316081 filed Oct. 30, 2002 is incorporated by reference.

What is claimed is:
 1. A display device comprising: a first display unithaving a display surface on a front surface thereof; a second displayunit having a display surface on a rear surface thereof; and a commonillumination unit interposed between the first display unit and thesecond display unit illuminating both the first display unit and thesecond display unit with light, wherein the illumination unit includes alight-guiding member including a first light-emitting surface oppositethe first display unit and a second light-emitting surface opposite thesecond display unit, and wherein a transflector is interposed betweenthe second light-emitting surface of the light-guiding member and thesecond display unit.
 2. The display device of claim 1, wherein thedisplay area of the first display unit two-dimensionally overlaps thedisplay area of the second display unit and an area outside the displayarea of the second display unit.
 3. The display device of claim 2,wherein the transflector has different optical characteristics betweenan overlapping portion two-dimensionally overlapping the display area ofthe second display unit including: a region two-dimensionallyoverlapping between the transflector and the display area of the firstdisplay unit; and a portion of the region.
 4. The display device ofclaim 1, wherein the transflector further comprises a light-diffusingtransflector.
 5. The display device of claims 1, wherein thetransflector further comprises a thin film including a reflectivematerial and has a light transmitting thickness.
 6. The display deviceof claim 1, wherein the transflector further comprises a thin filmincluding a reflective material and has a plurality of fine lighttransmitting apertures dispersed therein.
 7. The display device of claim1, wherein the transflector comprises: a base member comprising a lighttransmissive material; and a light-diffusing layer having fine particlesdispersed in the base member, the light-diffusing layer comprising alight transmissive material having a different refractive index fromthat of the base member.
 8. The display device of claim 1, wherein thetransflector comprises: a base member comprising a light transmissivematerial; and a light-diffusing layer having fine particles dispersed inthe base member, the light-diffusing layer comprising a reflectivematerial.
 9. The display device of claim 1, wherein a light diffuser isinterposed between the first light-emitting surface of the light-guidingmember and the first display unit.
 10. An electronic apparatuscomprising: the display device of claim 1; and a controller forcontrolling the display device.